1. Field of the Invention
The present invention relates to the application of electro- or magneto-rheological fluids to the dampening of vibration in a barfeeder. The invention is also directed to an improved barfeeder.
2. Brief Description of the Prior Art
A considerable segment of the metalworking manufacturing industry pertains to turning. In this process a metalworking lathe spins bars of various lengths and diameters at the appropriate revolutions per minute while cutting the workpiece with a tool to the specified shape or diameter. Metalworking lathes are driven mechanically by cams and other mechanical devices or electronically with the use of CNC (computer numeric control) and may be configured with a sliding or fixed headstock (spindle). The process has become accepted worldwide, is used in one form or another in most metalworking industries and variations on the process abound.
In turning, application engineers and their associated counterparts determine the best way to manufacture a particular part. Some parts are cast and then turned and drilled but this requires that each part be individually loaded into the lathe. Many manufacturers opt to form the part, if possible, from barstock as it can be continuously fed into the lathe with a barfeeder.
A barfeeder pushes a bar of selected diameter to the specified part length into the workspace of the lathe for part production. After the part is worked to completion and cut off, the lathe chuck automatically opens, signaling the barfeeder to push the bar material to the next working length and the cycle thus repeats.
In simplest form, a barfeeder requires an operator to manually reload the next bar of material for working. Taking automation one step further, a device called a magazine barloader not only feeds the bar material into the lathe, but also automatically reloads the next bar length providing a continuous supply of material to the lathe without operator intervention.
The North American standard length for barstock is 12 feet. Shops want to run their bar machines as fast as possible, typically at speeds in excess of 5,000 to 10,000 rpm, to achieve high production rates. Although a certain amount of the material is supported within the headstock or spindle of the lathe, the remainder of the material must be supported in the barfeeding device. As the rotating speed of a 12-foot bar increases, the barstock tends to whip and vibrate in the barfeeder, adversely affecting machining results.
There is a direct correlation between bar straightness and bar vibration experienced in the barfeeder. Steel manufacturers have responded to this need by refining their processes to provide straighter material to their turning manufacturing customers but non-ferrous materials are usually extruded as opposed to drawn (as most steels are) and the straightness cannot be as closely controlled. In addition, even if the barstock is straight when it leaves the manufacturer, it may be damaged in handling before it reaches the barfeeder of the turning customer. Hence vibration dampening in barfeeders remains as a big issue.
For precision production operations, vibration dampening is generally accomplished in one form or another (depending on the barfeeder manufacturer) by hydrodynamic suspension of the barstock in a guide channel mechanism with a heavy oil to dampen bar whip and vibration. This is generally effective until (1) the mass of the material (normally associated with diameter) overcomes the effective use of hydrodynamic suspension or (2) the bar straightness is out of the operational condition for this method of vibration dampening.
Hydrodynamic suspension in a barfeeding device is provided by a simple recirculating, non-pressurized flow of oil between the outside diameter of the spinning bar and the inside diameter of the guide channel to allow the bar to find its natural line of least resistance, which in a straight bar, is the center of the channel. This allows the bar of whatever length and diameter to spin at the required RPM silently and with no vibration. The oil should be of a viscosity to provide adequate hydrodynamic suspension but the barstock should spin relatively free of the oil in the transition area between the barfeeder and the lathe so as not to introduce tramp oil into the lathe coolant. The latter requirement prevents the use of heavier viscosity oils that may provide better vibration dampening qualities. When the mass of the bar material or the lack of straightness overcome the hydrodynamic suspension of the barfeeding device the lathe RPM must be reduced, compromising productivity, or quality is compromised.